/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet;

import java.io.IOException;

/**
 * Defines an object that receives requests from the client and sends them to
 * any resource (such as a servlet, HTML file, or JSP file) on the server. The
 * servlet container creates the <code>RequestDispatcher</code> object, which
 * is used as a wrapper around a server resource located at a particular path or
 * given by a particular name.
 * 
 * <p>
 * This interface is intended to wrap servlets, but a servlet container can
 * create <code>RequestDispatcher</code> objects to wrap any type of resource.
 * 
 * @author Various
 * @version $Version$
 * 
 * @see ServletContext#getRequestDispatcher(java.lang.String)
 * @see ServletContext#getNamedDispatcher(java.lang.String)
 * @see ServletRequest#getRequestDispatcher(java.lang.String)
 * 
 */

public interface RequestDispatcher {

	/**
	 * Forwards a request from a servlet to another resource (servlet, JSP file,
	 * or HTML file) on the server. This method allows one servlet to do
	 * preliminary processing of a request and another resource to generate the
	 * response.
	 * 
	 * <p>
	 * For a <code>RequestDispatcher</code> obtained via
	 * <code>getRequestDispatcher()</code>, the <code>ServletRequest</code>
	 * object has its path elements and parameters adjusted to match the path of
	 * the target resource.
	 * 
	 * <p>
	 * <code>forward</code> should be called before the response has been
	 * committed to the client (before response body output has been flushed).
	 * If the response already has been committed, this method throws an
	 * <code>IllegalStateException</code>. Uncommitted output in the response
	 * buffer is automatically cleared before the forward.
	 * 
	 * <p>
	 * The request and response parameters must be either the same objects as
	 * were passed to the calling servlet's service method or be subclasses of
	 * the {@link ServletRequestWrapper} or {@link ServletResponseWrapper}
	 * classes that wrap them.
	 * 
	 * 
	 * @param request
	 *            a {@link ServletRequest} object that represents the request
	 *            the client makes of the servlet
	 * 
	 * @param response
	 *            a {@link ServletResponse} object that represents the response
	 *            the servlet returns to the client
	 * 
	 * @exception ServletException
	 *                if the target resource throws this exception
	 * 
	 * @exception IOException
	 *                if the target resource throws this exception
	 * 
	 * @exception IllegalStateException
	 *                if the response was already committed
	 * 
	 */

	public void forward(ServletRequest request, ServletResponse response)
			throws ServletException, IOException;

	/**
	 * 
	 * Includes the content of a resource (servlet, JSP page, HTML file) in the
	 * response. In essence, this method enables programmatic server-side
	 * includes.
	 * 
	 * <p>
	 * The {@link ServletResponse} object has its path elements and parameters
	 * remain unchanged from the caller's. The included servlet cannot change
	 * the response status code or set headers; any attempt to make a change is
	 * ignored.
	 * 
	 * <p>
	 * The request and response parameters must be either the same objects as
	 * were passed to the calling servlet's service method or be subclasses of
	 * the {@link ServletRequestWrapper} or {@link ServletResponseWrapper}
	 * classes that wrap them.
	 * 
	 * 
	 * 
	 * @param request
	 *            a {@link ServletRequest} object that contains the client's
	 *            request
	 * 
	 * @param response
	 *            a {@link ServletResponse} object that contains the servlet's
	 *            response
	 * 
	 * @exception ServletException
	 *                if the included resource throws this exception
	 * 
	 * @exception IOException
	 *                if the included resource throws this exception
	 * 
	 * 
	 */

	public void include(ServletRequest request, ServletResponse response)
			throws ServletException, IOException;
}
